1. Field of the Invention
The present invention relates to a pneumatic actuator for a manipulator, and more particularly to a so-called air-bag type actuator with an elongate tubular body having an inner pressure chamber to be supplied with pressurized working fluid for causing longitudinal deformation of the tubular body.
2. Description of the Related Art
Various kinds of actuators for converting electrical energy or pressurized fluid energy into mechanical energy are known in the art, e.g. electric motors, hydraulic cylinder/piston devices, etc. However, there are many instances where it is undesirable or difficult to put these actuators into practical use.
For example, an ordinary electric motor tends to generate sparks and is sometimes dangerous in explosive environment as is typically the case in powder industry or oil industry. Besides, electric motor generally requires a reduction gear mechanism and cannot be directly connected to appliances to be driven by the motor. It is therefore difficult to improve the operational efficiency and reliability of the total system involving a motor. On the other hand, a hydraulic cylinder/piston device operated by pressurized working oil requires a careful control of the oil in terms of its temperature and purity, and becomes bulky in shape and/or size when a higher power output is required. The cylinder/piston device further encounters difficulties in effectively avoiding environmental contamination by completely preventing undesirable oil leakage.
In order to overcome the aforementioned problems, there has been proposed a pneumatic actuator as disclosed, e.g., in U.S. Pat. No(s). 4,615,260 and 4,860,639, both assigned to the assignee of this application. The pneumatic actuator according to these proposals includes an elongate tubular body of a rubber-like elastic material, with an outer circumferential wall and an inner pressure chamber. A braided reinforcing structure is arranged on the outer circumferential wall of the tubular body, and is composed of cords of high tensile strength fibers oriented at an initial braiding angle relative to the longitudinal axis of the tubular body, which is determined with reference to a so-called "angle of repose" of the braided structure. The axial ends of the tubular body are tightly closed by closure members, at least one of which has a connection hole for supplying pressurized fluid into the pressure chamber in the tubular body to cause an axial contraction or elongation of the actuator depending upon the initial braided angle of the reinforcing structure.
The pneumatic actuator of such a structure proved to be quite advantageous in that it is light in weight, smooth in operation, easy to control and free from environmental contamination, as compared with conventional actuators in the form of electric motors, hydraulic cylinder/piston devices, etc. Still, however, it is highly desirable to further enhance the versatile utility of the pneumatic actuator in terms of a reduced consumption of energy required for operating the actuator and more improved reliability in operation, while maintaining all the advantages mentioned above.